"Hey! Remember that Little Mermaid movie we made, a few years ago? Yes? Well, just in case you don't, here's a synopsis of its major scenes! Now available on Disney Blu-ray™!"
I'm of the opinion that when you make a dark ride, its content should dictate its form. Peter Pan's Flight, for example, uses miniatures and a suspended ride vehicle to simulate flying like Peter and friends. You could just as easily make Peter Pan's Flight into a Dumbo's Flight ride, and it would be just as affecting.
Peter Pan's Flight isn't interested in telling the story of the film it's based on. It prioritizes the experience of flying over London and Neverland more than re-telling the film's story. It gives you an experience you can't get in front of a television set. It gives you an experience you can only get in Fantasyland.
Following this ideology (like WDI once did), I can think of two options for a Little Mermaid ride.
A submarine ride (a dark ride that's actually underwater). Since dance and fluidity of movement are so important to the movie, the challenge would be building animatronics that are graceful underwater, and not clunky like the ones in (20,000 Leagues Under the Sea / Finding Nemo's Submarine Voyage).
A dark ride that simulates being underwater. The challenge would be building animatronics, sets, and ride vehicles that believably adhere to underwater physics, while still maintaining the grace mentioned above. WDI has already toyed with this, set-wise, in the queue to the Seas with Nemo and Friends, so this isn't a revolutionary suggestion on my part.
Projecting a few bubbles on the walls and hanging metal overhead to look like currents don't quite cut it. Also, Ariel's beehive, lol. A for effort, fellas.
Ariel's Undersea Adventure is a soulless exercise. Its only successes are the movie's successes. Fortunately there are ample successes, since the Little Mermaid is a great film, but it's a shame that all of WDI's effort went into xeroxing a great film.
I shouldn't be harsh. I can't imagine how many Imagineers had to move to Ursula's garden after building this ride.